Letter to the Editor
I was interested to read the article by Bhargava and colleagues1 published in Sex Transm Dis. 2017 February. They mentioned that positivity of microscopy and culture was greater (P < 0.0001) in men with urethral discharge syndrome (65.8%) than in women with vaginal/cervical discharge (0.50%), indicating that basic diagnostic tests may not be cost-effective for diagnosis of vaginal/cervical discharge syndrome.1 This result has nothing to do with reliability.2–5 Reliability (precision) and validity (accuracy) are 2 completely different and important methodological issues. Regarding reliability, for quantitative variable intraclass correlation coefficient and for qualitative variables weighted κ should be used.
They mentioned that microscopy when compared with culture showed sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of 95.4%, 77.6%, 84.6%, and 95.3%, in men, whereas in women, it was 77.8%, 99.9%, 92.1%, and 99.9%, respectively.1 These estimates have also nothing to do with reliability and actually are a few estimates to assess validity of a single test. Considering the limitation of the mentioned estimates (sensitivity and specificity usually being used for public health purposes while PPV and NPV for clinical purposes. Moreover, PPV depends on the prevalence of the outcome and cannot be a good estimate to judge about the validity of a single test. Why did the author not use likelihood ratio positive and likelihood ratio negative as well as diagnostic accuracy [(both true positive and true negative results/total) × 100] and odds ratio (true results/false results), preferably more than 50, to evaluate the validity of microscopy compared to culture?2–5
As a take home message, for reliability and validity analysis, appropriate tests should be applied by researchers. Otherwise, misdiagnosis and mismanagement of the patients cannot be avoided.
Siamak Sabour, MD, MSc, DSc, PhD
Safety Promotion and Injury Prevention
and Department of Clinical Epidemiology
School of Health
Shahid Beheshti University
of Medical Sciences
Tehran, I.R. Iran
1. Bhargava A, Bala M, Singh V, et al. How reliable is microscopy and culture for the diagnosis of gonorrhea? An 11-year experience from INDIA. Sex Transm Dis 2017; 44:111–113.
2. Szklo M, Nieto FJ. Epidemiology Beyond the Basics. 2nd ed. Manhattan, new York, United State: Jones and Bartlett Publisher, 2007.
3. Sabour S, Ghassemi F. The validity and reliability of a signal impact assessment tool: statistical issue to avoid misinterpretation. Pharmacoepidemiol Drug Saf 2016; 25:1215–1216.
4. Sabour S, Ghassemi F. Accuracy and reproducibility of the ETDRS visual acuity chart: methodological issues. Graefes Arch Clin Exp Ophthalmol 2016; 254:2073–2074. Epub 2016 Jul 5.
5. Sabour S. Validity and reliability of the new Canadian Nutrition Screening Tool in the ‘real-world’ hospital setting: Methodological issues. Eur J Clin Nutr 2015; 69:864.